The problem begins when you need exposition to explain the motives of your characters. If you don't provide enough information, you risk making your characters seem erratic, illogical, inconsistent, non-believable.
Ah, yes. I agree that the
plot of each individual branch needs to be a linear progression that stands on its own. Pretend the other branches don't even exist.
I don't think I've ever read any of your work, so I can't do any better than some educated guesses. That said...
If you keep having to establish the same motives, purpose, ethics of your characters, maybe you're branching too early, before you've established the points that underpin multiple branches?
Or maybe your branches are too similar, causing the same kinds of situations to crop up over and over again? If in branch A your character has to choose between fighting a dragon head-on or sneaking into its lair, and in branch B between setting off a bar brawl or cooling tensions, and in branch C between becoming a mercenary or, I dunno, the royal gardener, then yes, you have to keep motivating whether or not they prefer solving their problems with violence, but only because you keep presenting them with yes-violence no-violence problems.
Or maybe you're still trying to explain too much? The actions of your characters are
themselves explorations of their motives, desires, and beliefs. If Mandy knocks over Johnny's beer and he retaliates by pummelling her mercilessly, it's not
required to examine how he got to be so violent. It can be sufficient to establish that he just
is, depending on what his role in the story is and what kind of story you're writing.
If I'm still way off the mark, then could you give some concrete examples of what you're struggling with?